Steady-State Hydrodynamic Power Attenuation by Finned-Buoys

Abstract

Results of experimental and computational fluid dynamics (CFD) studies conducted to compare the flow-energy-attenuating performances of two different buoy configurations are presented. A finned-body was experimentally studied in two orientations—one with a splitter and one in a 22.5 deg yaw orientation (with no splitter). The finned-buoy is designed for both wave and current attenuation; however, only the current application is discussed here. Scaled models were subjected to wind tunnel testing and CFD analyses. For this study, the steady-state drag coefficient (CD) is considered to be the performance measure. The CFD model is used to match the physical testing by utilizing the k–ω turbulence model. Reynolds numbers (based on the tip-to-tip fin diameter) approaching the drag crisis are used to evaluate the bodies of interest, both of which have an aspect ratio (draft-to-diameter) of 1.85. The finned-bodies do encounter a drag crisis (as commonly seen with a cylinder), since the fins cause the buoys to act as a bluff body. The flow structures around the bodies are examined and compared to those predicted by established theories. For the finned-body, the 22.5 deg yaw orientation is found to have a consistently higher drag than the splitter orientation. The drag enhancement is explained by two phenomena. The first is a low-pressure area located in pockets adjacent to the upstream fins. The second is the absence of the drag-crisis, due to fixed separation points at the fin tips for all Reynolds numbers.